1. Field of the Invention
The invention concerns methods and devices for medical imaging. The invention in particular concerns such methods and devices with which a registration of images that were acquired with different imaging modalities is possible.
2. Description of the Prior Art
Several different imaging methods are used in medical engineering. Among these are, for example, computed tomography, magnetic resonance tomography, ultrasound and positron emission tomography. These imaging modalities deliver spatially resolved information about different physical properties of an examined region of an examination subject. Since different imaging modalities can provide information about different properties of the examined region, it is desirable to acquire image data with different imaging modalities.
In imaging of an examined region with multiple imaging modalities, the registration of different acquired images with respect to each other is a requirement. A registration requires that the images acquired with different imaging modalities be aligned and correctly scaled in a suitable manner. Due to the different physical processes on which the different imaging modalities are based, different perturbations can be present in the images acquired with different imaging modalities. For example, an image acquired with a magnetic resonance imaging device can have perturbations due to nonlinearities of gradient fields, with such perturbations not being present in an image of the same region that is acquired with an ultrasound imaging device.
For registration of images that have been acquired with different imaging modalities, user-defined anatomical landmarks can be identified in different images. For example, bones or catheters can be used as landmarks. However, such landmarks are linked to a position in the case of a bone, or in the case of the catheter can merely be invasively positioned and be dependent on the anatomy of the patient. A user-defined landmark establishment can be time-consuming. Depending on the experience of the user, a user-defined establishment can be imprecise or error-prone if the user cannot reliably identify anatomical landmarks. It can be difficult to determine a sufficiently high number of registration points in order to be able to produce a nonlinearity for registration in three dimensions. The number of anatomical landmarks that can easily be recognized in images may be too few for such purposes.
US 2010/0087727 A1 and DE 10 2008 047 644 A1 describe a method and a combination system in which a registration of images acquired with different imaging modalities is implemented depending on a thermal information. This requires a corresponding detectable heating of the examination subject.
There still exists a need for methods and devices for imaging in which a reliable co-registration of images acquired with different imaging modalities is possible in order to be able to fuse information acquired in the various image data with one another.